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SubjectRe: [PATCH 2/2] x86/head_64.S: Pass struct boot_params' virtual address to C

* Borislav Petkov <bp@alien8.de> wrote:

> From: Borislav Petkov <bp@suse.de>
>
> ... so that callees don't have to convert it and can use it directly.
> Simplifies C code a bit. Cleanup comments and formatting in the
> vicinity, while at it.
>
> Also, document what phys_base really is.
>
> No functionality change.
>
> Signed-off-by: Borislav Petkov <bp@suse.de>
> ---
> arch/x86/kernel/head64.c | 8 ++++----
> arch/x86/kernel/head_64.S | 10 +++++++---
> 2 files changed, 11 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
> index 54a2372f5dbb..17ee20a9b4e4 100644
> --- a/arch/x86/kernel/head64.c
> +++ b/arch/x86/kernel/head64.c
> @@ -118,7 +118,7 @@ static unsigned long get_cmd_line_ptr(void)
>
> static void __init copy_bootdata(char *real_mode_data)
> {
> - char * command_line;
> + char *command_line;
> unsigned long cmd_line_ptr;
>
> memcpy(&boot_params, real_mode_data, sizeof boot_params);
> @@ -130,7 +130,7 @@ static void __init copy_bootdata(char *real_mode_data)
> }
> }
>
> -asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
> +asmlinkage __visible void __init x86_64_start_kernel(char *real_mode_data)
> {
> int i;
>
> @@ -163,7 +163,7 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
> set_intr_gate(i, early_idt_handler_array[i]);
> load_idt((const struct desc_ptr *)&idt_descr);
>
> - copy_bootdata(__va(real_mode_data));
> + copy_bootdata(real_mode_data);
>
> /*
> * Load microcode early on BSP.
> @@ -180,7 +180,7 @@ void __init x86_64_start_reservations(char *real_mode_data)
> {
> /* version is always not zero if it is copied */
> if (!boot_params.hdr.version)
> - copy_bootdata(__va(real_mode_data));
> + copy_bootdata(real_mode_data);
>
> x86_early_init_platform_quirks();
>
> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
> index ac9d327d2e42..506de36293bc 100644
> --- a/arch/x86/kernel/head_64.S
> +++ b/arch/x86/kernel/head_64.S
> @@ -266,9 +266,12 @@ ENTRY(secondary_startup_64)
> movl initial_gs+4(%rip),%edx
> wrmsr
>
> - /* rsi is pointer to real mode structure with interesting info.
> - pass it to C */
> - movq %rsi, %rdi
> + /*
> + * %rsi is pointer to real mode struct boot_params with interesting info.
> + * Pass its virtual address to C.
> + */
> + movq $__PAGE_OFFSET_BASE, %rdi
> + addq %rsi, %rdi

The updated comments and other details are fine, but I'm not sure about the __va()
change: the patch essentially open codes __va() in assembly - which would make any
changes to __va() [for whatever reason] more difficult, right?

Right now we don't seem to have a single such line of assembly, so changes to
__va() can be done in C alone.

Thanks,

Ingo

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